Smell is a sensory modality that can generate strong emotions but is rarely used within virtual training environments. As the most evocative of our senses, smell can be used to contrast or heighten particular emotional effects, and provide an increased sense of richness or fidelity to a virtual scene. Our sense of smell differs from sight and sound in two important ways. First of all, we smell by means of an actual intake of molecules with which our body interacts. Thus it is a chemical sense (as is taste). Secondly, smell is first processed by the emotional parts of the brain, and is rationally analyzed only after some delay (Pine, 1995, Howard Hughes Medical Institute Report, pp. 48-55). Both these aspects have implications for smell's use within training environments.
However, smell is probably the least explored and understood design challenge in a virtual environment, although it promises much in regard to its power to augment emotional experience, including emotional experiences in virtual environments. As such, there is an ongoing need for scent delivery devices that can be used to enhance emotional experiences, especially emotional experiences in virtual environments.